1. Field of the Invention
The present invention relates to an image processing apparatus and method and, more particularly, to an image processing apparatus and method, which extract an image feature portion from color image data electrically read based on an original image or color image data created by a computer, and process color image data to be output to, e.g., a printer on the basis of the extraction result.
The present invention relates to an image processing apparatus and method and, more particularly, to an image processing apparatus and method, which smoothes a bit map image data showing character and figure output by external equipment.
2. Description of Related Art
In recent years, a color printer apparatus which obtains color images by outputting digitally processed color image data, and a color image printing system such as a so-called digital color copying machine, and the like, which color-separates and electrically reads a color original image, and obtains a copy of a color image by printing out the read color image data onto a recording paper sheet have evolved remarkably. As such apparatuses prevail, requirements for image quality of color images are becoming stricter, and especially, requirements for printing black characters and lines more clearly and sharply are becoming stricter. More specifically, when a black original image is color-separated, yellow, magenta, cyan, and black signals are generated as those for reproducing black. When printing is done directly based on the obtained signals, since black is reproduced by superposing these four colors, a black thin line produces smear due to slight misregistration among the colors. As a result, black does not appear black or is blurred, thus considerably deteriorating the print quality.
On the other hand, in one method, information associated with black, color information associated with colors, and feature data of the spatial frequencies of thin lines, dot patterns, and the like are extracted from an image signal representing an image to be processed to detect, e.g., areas for black characters, color characters, and the like, and to also detect areas for a halftone image, dot pattern image, and the like, and image processing suitable for each detected area is done so as to express, e.g., black characters using black alone. Also, in another method proposed, a plurality of different thicknesses of characters and lines can be discriminated, and the color amount of black is adjusted or character and dot pattern edges are separately detected in accordance with the thicknesses of characters to execute different image processing operations for character edges in a dot pattern/halftone image or white background, thus attaining smooth black character processing. However, even after image area separation, since a printer having a resolution of about 400 dpi has a dot spacing of 63.5 microns, character and figure edges formed by dots look shaggy with the visual sense of a human being, that can distinguish up to about 20 microns, and the print quality is not so high.
In order to improve the print quality, a system shown in FIG. 32 is known. In this conventional system, a page layout document for DTP, wordprocessing or graphic document, or the like is created using a host computer 1310, and is printed out by a color printer (laser beam printer) via a raster image processor 1313. Reference numeral 1311 denotes an application program running on the host computer 1310, and for example, wordprocessing software such as “Word” (trademark) available from Microsoft Corporation, page layout software such as PageMarker (trademark) available from Adobe Corporation, and the like, are popularly used. A digital document created by such software is sent to a printer driver 1312 via an operating system (OS; not shown) of the computer. This digital document is normally a set of command data that represent figures, characters, and the like in one page, and these commands are sent to the printer driver 1312. The commands are expressed as a language system called a PDL (page description language), and GDI (trademark), PS (PostScript: trademark), and the like are typical PDLs. The printer driver 1312 transfers PDL commands output from the application 1311 to a rasterizer 1314 in the raster image processor 1313. The rasterizer 1314 maps characters, figures, and the like expressed by the PDL commands to an actual two-dimensional bitmap image to be printed out. The rasterizer 1314 uses a frame as a two-dimensional plane, and forms the bitmap image over the entire frame by one-dimensionally repetitively scanning (rasterizing) in units of lines. The bitmap image mapped by the rasterizer 1314 is temporarily stored in an image memory 1315.
A document image displayed on the host computer 1310 is sent as PDL commands to the rasterizer 1314 via the printer driver 1312, and the rasterizer 1314 maps a two-dimensional bitmap image onto the image memory 1315. The mapped image data is sent to a color printer 1318. The color printer 1318 mounts a known electrophotographic image forming unit 1319, which prints out the image data by forming a visible image on a recording paper sheet. The image data in the image memory 1315 is transferred in synchronism with sync signals and clock signals required for operating the image forming unit 1319, or a specific color component signal, its request signal, and the like.
Smoothing is known as a technique for improving the print quality by removing shagginess or staircasing of character and line image edges. However, no conventional method of satisfactorily smoothing multi-color, multi-valued image data is available.
When full-color image data transferred from an external equipment includes both character and picture data, its image quality can be further improved using an adaptive processing circuit which is mounted on, e.g., a color copying machine or the like. However, character areas cannot always be detected 100% by image area separation, and may be erroneously detected in a natural image area, resulting in poor reliability.
When characters and figures created by a personal computer are printed out as monochrome images using a 400-dpi printer, for example, if an image described in a page description language is rasterized, staircasing inevitably remains. In case of a color printout, since image data that places an importance on gradation may be simultaneously transferred, if the resolution of such image data is also increased by smoothing in the same manner as in other areas, the image quality deteriorates.